Microlenses are used in a wide range of devices, such as copy machines, optical memory and/or laser disk systems, to focus, collimate or otherwise shape light. They typically range in size from 0.1 to 1 millimeteis (100-1000 .mu.m), although they can be considerably smaller or larger. Microlenses can be produced as objects on substrates, typically broadly describable as protrusions in the general shape of a dome or spherical segment, or as regions of modified refractive index (gradient indices) within substrates. Such microlenses have been made by a number of methods, including ion exchange, chemical vapor deposition (CVD), electromigration, photolithography or organic photoresist, diffusion polymerization, and various other techniques. Some of these methods are described in Fundamentals of Microoptics; Distributed-Index Microlens, and Stacked Planar Optics, by K. Iga, Y. Kohubun and M. Oikawa, OHM, Academic Press Japan, Inc. Tokyo, 1984, US Edn. Academic Press, Orlando, Fla. (ISBN-0-12-370360-3). Among many scientific publications and other disclosures in the field are those referred to in the above cited book as well as others such as the article "Microlenses for Coupling Junction Lasers to Optical Fibers," by L. G. Cohen and M. V. Schneider, Applied Optics, 13, pp 89-94, January 1974.
The uses for microlenses include collimating light from a laser diode (LD) or light emitting diode (LED) through a material or into an optical fiber as shown in FIGS. 1 and 2. Other uses for microlenses also include focusing light. These collimating and focussing effects can be used to collimate light or focus light into a waveguide or onto a spot at a distance determined by the shape of the lens and the refractive indices of all elements in the optical path for the light at issue.
The currently available microlenses tend to fall into the three categories: (1) gradient index planar lenses; (2) protruding structures formed of inorganic oxide glasses; and (3) protruding structures formed from materials which deform or decompose at relatively low temperatures, such as thermoplastic or other organic based materials. This invention concerns microlenses of the second type. Recent examples of the second type, protruding structures formed of inorganic oxide glasses, tend to be expensive, difficult to make, and limited in their range of refractive index and selective light absorption (filtering).
In one aspect, the invention relates to a method for producing a microlens on a substrate. The method involves the preparation of a carboxylated silicone precursor composition, application of the precursor composition to the surface of a substrate to form a precursor droplet; and, then the thermal oxidation of the precursor droplet to form a microlens. The substrates include but are not limited to composition of silica, silicates, borosilicate glasses and silicon.
Accordingly, it is an object of the invention to produce microlenscs in novel manner and to achieve controllability of the refractive index of the lenses through the introduction of germanium and various metal ions into the glassy microlenses.
A further object of the invention is to add metal ions to the microlens compositions for selective absorption of light and to achieve filtering properties of the microlenses.
These and other objects and features of the invention will be apparent from the following summary and description of the invention and from the claims.